In general, because of the movement of elevators, air inside hoistways flows at high speed around cars, thus generating noise while the elevators are in operation. The noise increases as the gap decreases between the inner surface of the hoistway and a side surface of a car and as the area increases where these two surfaces face.
Also, when a plurality of elevators are arranged, structures have been proposed, for example, in which two elevators are arranged in one hoistway in order to conserve the space of the hoistway. However, when the two elevators move in parallel (in the same direction and close relative positions), noise and vibrations increase markedly. Since such noise makes passengers uneasy, and is unfavorable in terms of operation, various proposals have been made for preventing parallel movement to solve the noise problem.
FIG. 4 is a view illustrating a conventional method of controlling elevators disclosed in, e.g., Japanese Patent Publication No. 54-14381, and shows the relationship between the positions of elevators and the amount of time elapsed since the elevators started. In the drawing, the transverse axis indicates time t[sec], and the ordinate axis indicates the distance h[m] in a direction in which the elevators move. A, C.sub.1 and C.sub.2 are curves indicating the movement of the elevators when they are accelerated, whereas B.sub.1 and B.sub.2 are curves indicating the movement of the elevators when they move at a constant speed.
In this case, on the basis of circumstances for other parallel elevators, the time is controlled when an elevator at rest starts from a position O at time t.sub.0 so that no other elevators move in the same direction in a range within which this elevator will move. Similarly, the time when other elevators start is controlled in relation to the other elevators moving in the same direction.
For instance, the elevator starting at time t.sub.0 from the position O (starting point) is accelerated and moves as indicated by a curve A, and elevators starting from positions .alpha..sub.1 and .alpha..sub.2 are accelerated and move as indicated by the curves C.sub.1 and C.sub.2. On the other hand, elevators passing positions .beta..sub.1 and .beta..sub.2 at a rated speed move as indicated by curves B.sub.1 and B.sub.2 (which become straight lines in this case).
Here, under a certain condition no elevator can approach another elevator at high speed when the latter elevator starts at time t.sub.0 within a distance H[m], wherein the distance H[m] refers to a distance within which two parallel elevators are allowed to approach each other. Conditions satisfying such a condition will be considered.
At this time, if both the distance between the position O and the position .alpha..sub.2, and the distance between the position .alpha..sub.1 and the position O are expressed as H[m], and if the distance between the positions .beta..sub.1 and .beta..sub.2 is expressed as 2H[m], then the condition under which there is no elevator between the positions .beta..sub.1 and .beta..sub.2 at time t.sub.0 when a certain elevator starts is sufficient. Also, when an elevator is detected in relation to the speed and position of another elevator, the condition under which there is no elevator which moves at a rated speed between the positions .beta..sub.1 and .beta..sub.2 is sufficient, and the condition under which there is no elevator which is just about to start between the positions .alpha..sub.1 and .beta..sub.2 is sufficient.
However, in such a control method, the range (see the shaded portion) within which the elevators may be detected is wide, and even an elevator away from the allowable approach distance H[m] may also be detected. Furthermore, even if the detection range is narrowed in relation to the speed and position, a determination must be made whether other elevators are moving in the rated speed or whether they are just about to start, thus complicating conditions. In addition, as shown in the drawing, the range within which the elevators move in parallel varies according to their speed and position, thus making it difficult to obtain an appropriate detection range.
In the conventional method of controlling elevators, as described above, the range within which parallel movement of elevators may be detected is wide, and conditions are complicated, thus making it difficult to set an appropriate detection range. Therefore, the detection range and the time during which the elevators are prevented from starting cannot be minimized. There is a problem in that the operation of elevators is adversely affected, thus making passengers uneasy while elevators are prevented from starting.